Ice dams, explained
What an ice dam is, and what to do about it
An ice dam is a ridge of ice at the eave that traps meltwater behind it. It looks like icicles, and it is a heat problem inside the house.
Icicles by themselves are not damage. A dam that keeps growing, or water that shows up on a ceiling or an outside wall, is the point to call.
What it can look like
Icicles and ice along one side of the roof, more than the others
A ridge of ice at the eave with water behind it
Stains on the ceiling near an outside wall
Frost on the nail tips in the attic, or wet insulation
In the attic
What we look for in the attic
Six things, in the order we check them.
Warm air leaks
Around the hatch, recessed lights, chimney chases, wire holes and plumbing stacks.
Insulation depth
Thin spots, gaps along the eaves and insulation pushed aside or compressed.
Blocked intake
Insulation packed against the roof deck at the eave, so no air can come in.
Exhaust
A ridge vent, gable vents or none at all, and whether they match the intake.
Frost and stains
On the nail tips and the underside of the deck, which show where damp air collects.
Bath fans and dryers
Vented outside through the roof or wall, not left open in the attic.
No soffit
The no-soffit fix, step by step
The attic needs cold air coming in low and going out high. When there is no soffit, we move the intake to the eave edge.
- 01
Step 1: Look at the rafter bays
From the attic we check how much room there is between the insulation and the deck at the eave.
- 02
Step 2: Choose the intake
A vented drip edge or small fascia vents, whichever suits the roof edge and the shingles.
- 03
Step 3: Fit baffles
One in each bay holds the insulation back and leaves a path for the air.
- 04
Step 4: Open the top
A ridge vent, cut to the length of the ridge, lets the air out.
- 05
Step 5: Seal the floor
The hatch, lights and pipe holes get sealed, so less heat goes up in the first place.
The year
A roof year in Bangor
When each kind of work fits. The dates move with the weather.
September – October
The busy months. Attic checks, ventilation work and re-roofs before the snow.
November
Tune-ups and the last re-roofs. Shingles seal poorly below 40°F, so cold days push jobs back.
December – January
The winter leak line opens and stays open through March. Steaming when a dam lets water in.
February – March
Dams are at their worst. Prevention waits for dry weather unless water is coming in.
April – May
Meltwater shows what the winter did. Leak repair and flashing.
June – August
Dry weather. The best time for ventilation work and re-roofing.
Questions
Ice dam questions
What causes an ice dam?
Heat from the house gets into the attic and warms the roof deck, so the snow on the roof melts from underneath. The meltwater runs down to the eave, which stays cold, and freezes there. Steam takes the dam off. Sealing the air leaks, adding insulation where it is thin and letting cold air through the attic is what keeps it from forming.
What does attic ventilation do?
It lets cold outdoor air in low, at the eaves, and out high, at the ridge, so the roof deck stays close to the temperature outside. That keeps snow from melting unevenly, and it carries off damp air. Poor ventilation can also affect some shingle warranties.
Should I chip the ice off myself?
No. Chipping, salt and a hammer damage shingles, and a fall from a ladder on ice is the real risk. If water is coming in, call us. We use low-pressure steam, from the ground or a lift where we can, and we won't go onto an iced roof without a way to tie off.
Will you look in my attic?
Yes, every visit starts there if we can get in. We check the air leaks at the hatch, lights and pipes, the insulation depth, the vents at the eaves and the ridge, and the underside of the deck for stains and frost.
Want someone to look in the attic?
Book the visit. We look at the attic, then the roof, and write it down.